The invention relates to a process for the preparation of copolymers of carbon monoxide with one or more ethylenically unsaturated compounds.
The preparation of copolymers of carbon monoxide and one or more ethylenically unsaturated compounds, in which copolymers the units originating from carbon monoxide substantially alternate with the units originating from the ethylenically unsaturated compounds, has been described in numerous patent publications.
Typically the preparation of the said copolymers is carried out as a liquid phase copolymerization process, whereby the monomers are contacted with a catalyst composition in the presence of a liquid non-polymerizable diluent. The formed copolymers are isolated, for instance, by filtration or centrifugation. Pure diluent is recovered from the remaining liquid, suitably by distillation and can be recycled.
A process whereby the polymerization proceeds in solution or suspension is described e.g. in EP 181,014. In this process the monomers react in the presence of a catalyst, being a complex compound obtained by reaction of a palladium, cobalt or nickel compound, an anion of a carboxylic acid with a pKa lower than 2, and a bidentate ligand.
Another liquid phase process for the preparation of the said copolymers is described in EP 235,865. In this process the catalyst composition is also based on a palladium compound and a bidentate ligand. However, instead of supplying an acid with a pKa lower than 2, a non-noble transition metal salt of the relevant acid is used. This reference discloses that replacement of the acid by the salt in some cases results in a considerable improvement in catalytic activity of the catalyst composition.
While salts of all non-noble transition metals are deemed to be included, special preference is given to salts of zirconium, vanadium, chromium, iron, nickel, copper, cerium, thorium and uranium.
It is further known that the preparation of linear alternating copolymers of carbon monoxide and one or more ethylenically unsaturated compounds can also be carried out in gas-phase operation. According to EP 248,483, the gas phase copolymerization offers considerable advantages, as regards reaction rate, molecular weight and bulk density, in comparison with the liquid phase process. Moreover, the recovery of the formed copolymers is simpler, because the filtration or centrifugation step can be omitted and no distillative removal of liquid diluent is required. When carried out on a technical scale, these advantages result in considerable cost savings.
The catalyst composition used in the gas-phase process is as disclosed in EP 248,483, also based on a palladium compound, an anion of an acid with a pKa of less than 2 and a bidentate ligand. It is stated that the anions may be incorporated in the catalyst composition either in the form of an acid or in the form of a salt. Eligible are salts of non-noble transition metals and main group metals. As very suitable are mentioned salts of zirconium, vanadium, chromium, iron, nickel, copper, cerium, thorium, uranium, aluminum, gallium, tin, lead and antimony.
In EP 248,843 acids and metal salts are disclosed as suitable alternative anion sources, and it is not alleged that by using a metal salt as anion source the catalytic activity of the composition will be enhanced which is in contrast to the findings according to EP 235,865 for liquid phase operation of the process.
In fact, further investigation of this aspect has shown that most of the metal salts, considered useful for enhancing catalytic activity in liquid phase operation of the process, including many salts of those metals, especially preferred for this purpose, do not have any promoting effect on the catalytic activity in gas phase embodiments of the process.
Surprisingly, it has now been found that the activity of catalyst compositions, used in gas-phase operations of the process, is significantly increased, if compositions are used which are based on specific cation sources, particularly in combination with specific anion sources.